FIG. 1 and FIG. 2 are an application circuit diagram of an existing linear constant current chip and a waveform graph of a working process thereof. A maximum voltage of a capacitor is a maximum output voltage of a rectifier bridge, and a minimum value exceeds a sum of a plurality of VF (Forward Voltage) values of LEDs in a plurality of LED string lights, which therefore requires a higher number of LEDs, and usually it requires about 80 LEDs for an application in 220V. When an input voltage rises/lowers, the voltage of the capacitor will also increase/decrease accordingly, in such a way, an efficiency of a system will change following a change of an input voltage. When the input voltage is very high, a power consumption of the chip will rise sharply, and both stability and reliability of the system will become worse.
Therefore, the current technology needs to be improved and developed.